Although epigenetic dysregulation is already recognized to play an important role in the initiation and progression of many types of cancers, studies on epigenetic cancer therapy have been primarily focused on targeting a single epigenetic regulator to disrupt the maintenance of the disease. The cross-talks between epigenetic pathways that dictate gene expression/silencing and therapeutic outcome are just beginning to gain recognition. This application has immediate clinical relevance since DOT1L inhibitors are now in clinical trials for individuals with MLL-r leukemia. Important clinical responses have been noted with DOT1L inhibitor treatment alone, but there is no doubt that combination approaches will be necessary. The objective in this application is to determine the critical epigenetic effectors and mechanisms that establish oncogene silencing in MLL-r leukemia upon DOT1L inhibition. Preliminary studies based on a genome-scale RNAi screen have identified an essential role of histone deacetylase Sirtuin 1 (SIRT1) in silencing DOT1L-dependent oncogenes in MLL-AF9 leukemia (published in Nature Medicine). This proposed study will further utilize genome-wide genetic and epigenetic research tools to dissect the epigenetic mechanisms underlying the expression and silencing of oncogenes in both MLL-r leukemia and normal hematopoiesis. The proposed application is INNOVATIVE, in our opinion, because it introduces a novel concept of combinational targeting that simultaneously induces and stabilizes epigenetic silencing for profound oncogene suppression. In addition, this research will be of SIGNIFICANCE because it immediately provides novel therapeutic opportunities against the difficult-to-treat MLL-r leukemias by simultaneously activating the oncogene silencing mechanisms. The Specific Aims of this proposal are: 1. Examine the direct effect of SIRT1 enzymatic activity on silencing DOT1L-driven oncogenes in MLL-r leukemia. 2. Evaluate the efficacy of SIRT1 and DOT1L combinational targeting as a novel therapeutic strategy against MLL-r leukemia. 3. Investigate the role of SIRT1 in silencing DOT1L-dependent genes in hematopoietic stem/progenitor cells. Dr. Chun-Wei David Chen is currently a Senior Research Scientist in the Department of Cancer Biology and Genetics at Memorial Sloan Kettering Cancer Center. Building on his scientific training in epigenetic regulation and experimental hematology, Dr. Chen uncovered and is now investigating the role of SIRT1 and DOT1L interactions in MLL-AF9 leukemia and normal hematopoiesis. His initial achievement identifies cross-inhibitory mechanisms between epigenetic pathways for cancer therapy was recently published in Nature Medicine. His long term goal is to provide novel opportunities for advanced cancer therapies by understanding how epigenetic regulators control gene expression under normal and malignant conditions. Dr. Chen will carry out his proposed project in a stimulating academic environment under the mentorship of Dr. Scott Armstrong, a recognized leader in the fields of leukemia genetics and epigenetics. Dr. Scott A. Armstrong has successfully helped two trainees who have obtained support through the NIH-K99 Career Development Award to obtain tenure-track faculty positions. He has proposed a career development plan to further Dr. Chen's scientific development and to help his transition to independence.